A video capturing a tender moment between an elderly man and his dying wife has gone viral this week.

The clip, uploaded to Facebook by Erin Solari earlier this month, shows the young woman’s 92-year-old grandfather Howard singing “You’ll Never Know” — a love song popular in the 1940s and 1950s — to his wife as he gently strokes her face.

The couple has been married for 73 years.

“Laura (Grandma) is at a hospice facility making peace with her final days,” Solari wrote in a video caption. “I was lucky enough to capture this precious, heart-melting moment between the two of them. Howard (Grandpa) is singing to her their love song, the song that comforted her when he went away to fight in World War II.”

In her post, Solari described how Howard and Laura used to sing the love song to each another during family gatherings.

“After 50 years of marriage, they renewed their vows and performed this song as a duet for the entire family at the reception,” she wrote.

Laura is now too weak to sing, which is why in the video she can only say the words to her beloved (at around the one-minute mark) before he chimes in with the rest of the song.

Solari also described her grandparents’ continuing adoration and affection for each other.

“Moments before this video began, when Grandma heard that Grandpa was in the room, she asked if she could hold him. Grandpa cannot stand on his own, but he immediately pulled his wheelchair close to her bed ready to make it happen. My cousin, Serena, who is a physical therapist, helped him to his feet and held him up throughout the entire song,” she wrote.

Although her grandmother is almost blind, that doesn’t “stop her from looking deep” into her husband’s eyes, Solari said.

The Facebook video has been watched more than 3.4 million times to date. On Sunday, Solari uploaded the clip on YouTube with added subtitles. She also included a message of gratitude to all the social media users who have been offering words of encouragement and support.

“The outpouring of love [has] lifted everyone’s spirits … including Grandma’s,” Solari wrote. “We all thank you so much for the love and kind words.”